The present invention relates to a compact, environmentally benign biological waste water treatment and disposal system.
Waste water, or sewage, produced from residential and commercial sources must be treated to remove environmentally adverse components prior to introduction into ground or surface waters. Significant health risks arise from human exposure to untreated waste water predominantly resulting from the presence of fecal coliform. While most cities and towns treat waste water by processing it through an active mechanical and chemical wastewater treatment plant, many xe2x80x9con sitexe2x80x9d residential treatment systems, primarily septic tanks, are used in rural or remote settings.
The first stage of xe2x80x9con sitexe2x80x9d treatment occurs at the septic tank, which serves as combined settling and skimming tank in which primary treatment of residential wastewater occurs. When water tight and structurally sound, a septic tank acts as an unheated, unmixed anaerobic digestion chamber where bacteria attacks and decomposes solids and particulate matter suspended in the waste water. The primary purpose of the septic tank is to separate solids, or sludge, from the liquids, and to provide storage for the sludge during the active decomposition process. As separation of the solids occurs, the liquid, or effluent, is passed to a secondary treatment stage.
A variety of secondary treatment systems have been used in conjunction with septic tanks, including, but not limited to: disposal fields, lateral lines, intermittent sand filters, recirculating granular-medium filters, and shallow-trench, sand-filled, pressure-dosed disposal fields. By far, the most common secondary septic treatment includes subsurface-soil absorption. A subsurface-soil absorption system, or leach field, consists of a series of narrow, relatively shallow trenches filled with a porous medium such as gravel. Porous material provides structure to the leach field, increases effluent water treatment, distributes effluent to the infiltrative soil surfaces and provides temporary storage capacity during peak flows.
Septic tank effluent is transported and applied to the disposal field by intermittent gravity flow or by periodic dosing by hydraulic pump or dosing siphon. Effluent discharged to the disposal field infiltrates into the soil primarily through the side-walls of the trench. Once effluent enters the unsaturated soil zone between the ground surface and the groundwater or bedrock, known as the vadose zone, flow is dictated by soil and bedrock conditions. Gravity will force the effluent over soil particle surfaces and within capillary pores where the effluent eventually finds its way into groundwater courses.
Groundwater contamination commonly occurs because effluent does not receive enough xe2x80x9ctreatmentxe2x80x9d between the septic tank and the groundwater course. It is common to find high fecal coliform levels in groundwater near septic tanks, leach fields and lateral lines. Typical disposal field treatment occurs as the effluent flows over and through the porous medium used in the disposal field trenches and as it infiltrates and percolates through the soil. Generally, the porous medium of the leach field acts as a submerged anaerobic filter under continuous inundation of effluent, and as an aerobic trickling filter under periodic application of effluent.
Intermittent gravity flow application of effluent in the leach field causes a biomat to develop progressively on any infiltrative surfaces. Once the biomat is in place, it serves as a biological treatment unit and as a mechanical and biological filter. Under this condition, the leach field environment is usually anaerobic due to relatively high organic and solid loading of the leach field. However, biological treatment occurs more rapidly under aerobic conditions than under anaerobic conditions. Therefore, it is usually desirable to use periodic dosing of waste water onto a large area leach field to prevent accumulation of a dense biomat. Periodic dosing facilitates maximum effluent treatment, under aerobic conditions, as the effluent moves through the coarse leach field material in a thin layer and through the soil vadose zone under unsaturated flow conditions.
Another effluent treatment method utilizes sand filters. Particularly, intermittent sand filters are shallow beds of sand provided with a surface oriented effluent distribution system and an underlying drainage system. Effluent from the septic tank is periodically applied across the surface of the sand bed where gravity pulls it downward through the sand where it undergoes physical, chemical and biological transformation. Suspended solids are removed by mechanical straining and sedimentation. Bacteria colonized within the sand grows by autofiltration and increases removal of suspended solids from the effluent. Microorganisms in the sand beds convert ammonia to nitrate and remove biological oxygen demand (BOD) under aerobic conditions. Anaerobic bacteria which coexist in the aerobic environment also bring about denitrification (conversion of nitrate to nitrogen gas) which results in significant loss of nitrogen from the effluent. While effective in secondary treatment of waste water, sand bed are difficult to maintain due to particulates clogging the filter which affects the aerobic condition of the site.
Lateral lines are yet another secondary effluent disposal method, quite similar in application to a leach field. Rather than having a leach field, trench or pit, pipes are connected to the septic tank and channel effluent into contact with the soil vadose zone. Usually, the lateral lines are filled with a porous medium such as gravel, and operate under the same principles as the leach field, albeit over a greater area. Due to the relatively small diameter of a lateral line pipe, typically 4 to 8 inches, it is often necessary to install a significant linear footage of the pipe to achieve the same magnitude of treatment which can be expected in a leach pit.
Often, between 200 and 500 linear feet of lateral line will be necessary to obtain acceptable treatment levels of septic tank effluent. This often requires accessing the land of an adjacent landowner to satisfactorily install and maintain lateral lines. Soils which are too porous provide insufficient treatment time and can result in contaminated effluent reaching groundwater. Soils which are not porous enough can diminish treatment effectiveness and result in incompletely treated sewage reaching the surface. Due to the endless variations of backyard soil conditions throughout the world, none of the currently available secondary treatment methods can be uniformly applied.
Quite often a shallow layer of soil over bedrock makes a leach pit or sand filter impractical. Likewise, a high groundwater table may make any of the conventional treatment methods undesirable and unsafe. Overflowing the treatment area will decrease the effectiveness of treatment and may result in diminishing microbial growth. Small parcels of property, such as are often found in rural towns financially incapable of installing and maintaining a treatment plant, may make lengthy lateral lines undesirable. Further, each of the conventional methods of treatment requires extensive excavation not only at the installation phase, but also in the event of failure, or for necessary periodic maintenance.
Further, each of these conventional disposal fields, leach fields, lateral lines and sand filters, tend to adversely impact the environmental under certain conditions, including: shallow soil over bedrock, exceeding quick or slow soil percolation rates, high groundwater levels, on steep slopes and where treatment must occur in a limited area. Under any of these conditions, effluent might reach the surface or groundwater before treatment occurs. The present invention achieves unexpected levels of treatment when compared to traditional systems.
It is desirable to have a system which is easy to repair and which needs little maintenance. Further, it is desirable to have a secondary treatment system which is not buried, as is common with leach fields and sand filters, so that it is not necessary to excavate the system to work on it. It is also desirable to have a treatment system which offers consistently predictable levels of treatment regardless of native soil conditions. Compact system dimensions are also desirable as it allows the system to be placed in a limited space, for example a small backyard. Typical lateral lines, or other known leach fields systems, require an easement or permission of the adjacent land owners to construct and access for repair and maintenance.
The apparatus and method of the current invention overcomes each of the stated problems and deficiencies of the known devices for providing secondary treatment waste water.
The present invention relates to a compact, environmentally benign onsite biological waste water treatment and disposal system installed down-flow from a conventional primary treatment process, such as a septic tank, and a conventional mechanical filter. More particularly, the present invention relates to an apparatus and method for the biological purification and natural disposal of liquid wastes using a secondary single pass trickling filter in conjunction with an evapotranspiration absorption (ETA) tertiary disposal bed. This invention replaces conventional secondary waste water treatment mechanisms, such as leach fields, sand filters and lateral lines.
It is preferred that both the secondary and tertiary systems are composed primarily of synthetic (man-made) materials, which may then be covered by various horticultural (plant and planting) materials. The synthetic materials utilized within the novel filter system are preferably synthetic textile materials which are inert, non-toxic, and non-biodegradable. Further, the synthetic materials would be fibrous masses having substantial surface area.
Within the secondary system, synthetic textile materials are housed in cylindrical structures. The cylindrical structures are contained within a housing, typically constructed of material which resist rapid decomposition, such as: wood, treated lumber, concrete blocks, plastic or fiberglass. The tertiary treatment system includes synthetic material loosely compacted within a housing similar in composition and configuration to the secondary system.
The trickling filter claimed herein is unique and advances the state of the art in several ways. First, the unique construction layout and extensive use of synthetic materials provides the surface area, aerobic action, and waste water treatment effectiveness of a large and expensive traditional sand filter, yet accomplishes the effect in a very compact filter unit at a fraction of the cost.
Further, the apparatus has far lower maintenance and cost of operation, as its design allows for pure gravity flow in most applications and ordinary use should necessitate little if any maintenance over extended periods of time. The apparatus is uniquely accessible so that even extraordinary major maintenance or repair can be easily accomplished without digging or the use of heavy equipment, which is a major shortcoming and expense associated with current predominant system types, such as leach fields and lateral lines.
By relying upon the synthetic material of the self-contained filter unit rather than native soils to provide secondary treatment, treatment can be optimized and made consistent for all users, even those residing in areas with soil properties which do not lend themselves to proper treatment of waste water and are currently either underutilized or an ongoing polluter. An advantage of the apparatus is that the trickling filter unit maintains full functionality and treatment effectiveness even with sporadic or intermittent use, contrary to current systems which often fail when sporadically used. This characteristic makes the apparatus a suitable solution for summer or vacation homes and cottages, hunting lodges, government recreational areas, and the like, which tend to have a high failure rate due to sporadic use.
Finally, by being designed specifically to allow for the utilization of construction materials which are also presently considered non-biodegradable waste products, such as scrap polypropylene and used automobile tires, the filter system is in a unique position of being able to offer a partial solution to the significant industrial waste disposal problems while providing cost effective and superior treatment of waste water addressing the global ground water pollution crisis.
The ETA tertiary disposal bed component also advances the state of the art and provides a unique, compact, economical, and practical method of treated effluent disposal. The current preferred method of combined treatment and disposal utilizes a leach field or lateral lines, with performance fluctuating from adequate to totally ineffective depending upon the local soil and environmental conditions. The nearest thing to a current remedy is to over-design the system, requiring ever more linear feet of buried lateral lines at relatively high cost of installation, virtually impossible maintenance, and poor utilization of space.
The ETA tertiary disposal bed of the present invention utilizes synthetic materials in conjunction with natural products to provide a far more consistent and effective effluent dispersal, while maintaining relatively low cost and ease of installation, minimal reliance upon unpredictable soil conditions, and far more compact installation. The compact size and minimized reliance upon native soils permits utilization of effective on-site sewage treatment on properties where traditional systems would be ineffective and/or unfeasible, while the use of synthetics and method of construction means that, in the rare case where maintenance or repair were necessary, it could be easily and cheaply accomplished without the need for further excavation or use of heavy equipment.
The secondary trickling filter and the ET tertiary disposal bed disclosed herein could be used separately or in a different configuration to augment an existing septic treatment system or to best suit site conditions and requirements. The combined use of natural and man-made materials, when properly constructed, produce an overall waste water treatment system that is cost effective, ecologically friendly, provides high levels of water purification, provides final disposal thereof, requires very little space, and is simple and relatively inexpensive to operate and maintain.
Further, testing shows that the system is very easy to maintain and does not have clogging problems such as those that often occur in other waste water filtering systems, particularly sand bed filters. The biological state of the trickling filter is easy to start and maintain, and in the event of contamination which compromises the aerobic treatment environment, correction can likely be made by simply flushing the system with neutralizing agent or water.
The treatment level achieved in waste water treated through the trickling filter and ETA bed is unexpected. Testing shows that fecal coliform levels of treated effluent are usually below testing limits and are significantly below the generally acceptable levels in treated municipal waste water effluent. Additionally, testing shows that nitrogen and phosphorus levels are below generally acceptable treated waste water limits, as are total suspended solids and biological oxygen demand (BOD). The benign treating environment also results in neutral pH of any treated effluent which eventually would reach ground or surface waters.